CALIBRATION AND STANDARDIZATION OF MICROWAVE-OVENS FOR FIXATION OF BRAIN AND PERIPHERAL-NERVE TISSUE

Rapid and reproducible fixation of brain and peripheral nerve tissue f or light and electron microscopy studies can be done in a microwave ov en. In this review we report a standardized nomenclature for diverse f ixation techniques that use microwave heating: (1) microwave stabiliza tion, (2) fast and ultrafast primary microwave-chemical fixation, (3) microwave irradiation followed by chemical fixation, (4) primary chemi cal fixation followed by microwave irradiation, and (5) microwave fixa tion used in various combinations with freeze fixation. All of these m ethods are well suited to fix brain tissue for light microscopy. Fast primary microwave-chemical fixation is best for immunoelectron microsc opy studies. We also review how the physical characteristics of the mi crowave frequency and the dimensions of microwave oven cavities can co mpromise microwave fixation results. A microwave oven can be calibrate d for fixation when the following parameters are standardized: irradia tion time; water load volume, initial temperature, and placement withi n the oven; fixative composition, volume, and initial temperature; and specimen container shape and placement within the oven. Using two rec ently developed calibration tools, the neon bulb array and the agar-sa line-Giemsa tissue phantom, we report a simple calibration protocol th at identifies regions within a microwave oven for uniform microwave fi xation. (C) 1998 Academic Press.